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Fdn. Drains Connect to Roof Drains

Fdn. Drains Connect to Roof Drains

Fdn. Drains Connect to Roof Drains

(OP)
What are some opinions regarding foundation and underslab (slab on grade) drainage systems that connect to roof drains that connect into the storm water system.  Are there concerns of backflow.  What if the existing storm line pipe is below the foundation/underslab drains?

Thanks

RE: Fdn. Drains Connect to Roof Drains

If you have deciduous trees nearby, don't do it. Blockage by fallen leaves getting into your drainage system is a real concern. If you must, perhaps you could oversize the pipes to reduce blockage, or provide plenty of cleanouts.

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RE: Fdn. Drains Connect to Roof Drains

As a general rule, I don't recommend it.  The potential for problems is too great.  However, if you really need to for various reasons, make sure that the main drain line is several feet below the floor/wall drainage system and oversizing the line as ACtrafficengr recommended is a good idea.

RE: Fdn. Drains Connect to Roof Drains

I have done this many times.  I have also not done it many more times. One of the usual problems I see is the roof piping tends to be undersized, sometimes greatly undersized. I typically use one conduit for roof runoff and a separate conduit for foundation/slab drains.

RE: Fdn. Drains Connect to Roof Drains

I have done this several times and has worked out okay.  The only problem that I could see is the possibility of trees or large shrubs that have root systems that could penetrate the drainage system.  However, most of the time it works just fine.  Just make sure you size the conduits accordingly.  

RE: Fdn. Drains Connect to Roof Drains

If you have expansive soils, you open the possibility of additional wetting.  That would be bad.

RE: Fdn. Drains Connect to Roof Drains

(OP)
Thank you for responses.  The concern was if the main storm sewers backup and resulted a back pressure this would exert a force (or possible hydrostatic force) on the foundation wall or slab on grade that could result in structural issues.

If we use a check valve on the foundation drain this would mitigate hydrostatic forces due to backflow water.

RE: Fdn. Drains Connect to Roof Drains

Put in a sump, that would handle overflow.  Pipe it so the invert into the sum is higher than the pipes of the poundation drain.

RE: Fdn. Drains Connect to Roof Drains

Check with your local municipality, many prohibit doing this because it adds unnessecary demand on the sewers and treatment process.

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